Prior art ventilators of reference in this specification, such as, for example, the one illustrated in FIG. 8 and labelled 100, comprise an axial fan 101 and an electric motor 102 for driving the fan.
The electric motor has a substantially cylindrical casing, a stator unit and a rotor unit, both housed in the casing, and a shaft protruding from the casing and rotationally driven by the rotor unit.
The fan has a connecting hub 103 coaxial with the shaft of the motor and a plurality of blades extending radially from the hub.
Usually, the fan hub is cup shaped, that is to say, it has a bottom wall 104 for connecting to the motor shaft and a substantially cylindrical lateral wall 105 from which the blades extend.
In order to limit the axial dimensions of the ventilator, the motor is at least partly housed inside the hub, surrounded by the lateral wall of the hub itself which extends from the bottom wall towards the motor.
A tubular gap 106 is defined between the motor casing and the fan hub, that is, between the casing and the lateral wall of the hub to allow the fan to rotate freely.
This type of ventilator has some disadvantages in heavy-duty applications such as agricultural machines or earthmoving machines.
In effect, in these applications, the performance of the ventilator may be seriously diminished by extraneous material such as straw, dust, soil, mud and so on, which finds its way into the gap 106 and prevents the fan from turning smoothly relative to the motor casing.
Under these circumstances, friction between the fan and the casing is increased, aeraulic performance is reduced and the motor may work with the rotor seized up and eventually break down.
To overcome these disadvantages, fans like the one described in patent EP1718872, to the same Applicant as this invention, have been developed. That patent relates to an axial fan where the bottom wall of the hub has openings in it from which the dirt that accumulates between the fan and the motor may be expelled during use.
In the event of prolonged use under heavy-duty conditions, however, the holes tend to become clogged, eventually bringing the fan to a stop.
In other prior art solutions, the fan hub is sealed and is defined by a box-shaped body.
Examples of hubs of this kind are described and illustrated in documents U.S. Pat. Nos. 2,664,961, 3,006,417, 3,904,314, 4,610,600, 3,231,022, 2,495,433, GB-A-630773 and GB-A-716389.
A detail of another prior art fan 101 is illustrated in FIG. 8a. In that fan, the hub 103 is defined by revolving a substantially T-shaped section 107.
In practice, the hub 103 is defined by a rigid disc 108 and an annular wall 109 connected at a middle portion of it to the disc 108.
The wall 109 forms a single part with the disc 108 and allows the blades 110 to be connected to the disc 108.
In this solution, too, however, as illustrated, gaps 111 are formed which are eventually filled by material such as mud, soil, sand and so on, leading to imbalance of the fan 101; the fan 101 illustrated in FIG. 8a also features reinforcement ribs 112.